Boiler in 105 year old home

SITUATION: 50 year old boiler running classic radiators on 100 year old house (converted into 8 apartments).

Boiler and pump kick in for 30 â€“ 100 seconds then turn off. Boiler pressure appears between 18 and 20. Temperature is well below 70 degrees.

When I first turned on the boiler, it kicked on and ran continuous til temp was attained and then cycled on and off. The temperature of the house was in the 50s when I started the boiler on Nov 1. Last year it appeared to be the same problem, but eventually the boiler gets hot enuff and heats appropriately (but with far too many cycles from my perspective). The system seemed to work best during the dead of winter when the boiler did not shut down for extended time during the day.

I have replaced no parts and the controls are without LEDS or schematics or troubleshooting information.

Could somebody point out what I should be looking into, I would like to be able to maintain the system myself and purchase appropriate replacement parts as needed.

Is there somewhere I can look to learn about the switched/sensors on the outlet and return piping and any other sensors as needed.

I am going to start by replacing the thermostat and go from there.

Is there some way to put a relay in front of the pump to delay its running for 1-2 minutes after the boiler ignites?

You can get a time delay relay, but it may not buy you anything. You'd probably get less shock to the system if the pump came on when the boiler lit. In fact, for max efficiency, the pump often runs when the boiler isn't lit.

For a boiler that old, it would be hard to tell what is going on,especially without any schematics.

On a modern boiler, there are numerous safety interlocks.
- minimum pressure to ensure you won't flash water to steam
- flame sensor to ensure you aren't running fuel but it is not lit
- max temp to shut it down if it gets too hot
This is not counting the mechanical things like a T&P valve.

Hard to say what yours has on it.

There may be a flame sensor on the gas valve that is shot...it tries to light and thinks the burner did not start, so it shuts off. Modern closed combustion boilers then go into a post purge to remove all fuel vapors, and then often will try again. A modern controller won't keep doing this forever, and gives up after a few tries. They often do a pre-burn purge, too, just to be safe.

I'm not a pro, but I'd look at the thermocouple that senses the flame is on...seems like it is trying to start, but doesn't think the burner actually lit, assuming yours has one.

That sure sounds like there is a problem. Short cycling like that is a "bad thing".

You mentioned a pump so I assume it is hot water heat. With a 50 year old boiler you should look at the cost benefit of a new boiler. You are probably very lucky if you get 50% efficiency out of the existing boiler. Modern condensing units reach 98 99%. The existing boiler is also probably oversized. Have you done any tightening up/insulation since the last time it worked right?

Get a heat loss done for the building. Upgrading insulation and sealing could also get you a real cost savings.

You said "the" thermostat. Doing something to allow control in each apartment might also be a good thing. Do some of the tenants keep windows open in the winter because it gets too hot?

The boiler may be cycling because of a control other than the thermostat. It could shut off for over temperature. You might want to check to see if people have turned down the flow to their radiators because of overheating. The boiler probably has a large volume of water and if the pump shuts off when the boiler shuts off, overtemp with the cycle times you listed may not be it. If the pump keeps going then the probablilty is higher of over temp cycling.

Here is some additional information and thanks for all of your input so far.

First a boiler upgrade may be in the future but is at least 2 years out.

Unfortunately almost ALL valves are frozen in individual apartments so little if any adjustment is made.

Yes to the hot waterâ€¦my apologies for not mentioning this.

â€¦â€œthe pump often runs when the boiler isn't litâ€â€¦

I might note that the pump and the flame run in unison. That is one NEVER RUNS WITHOUT the other. â€¦..I donâ€™t know if this is normal due to my lack of experience with these systemsâ€¦.but note that the pump never runs past the time that the boiler flame kicks off. A lot of heat seems to get wasted in the boiler.

Regarding insulationâ€¦..Iâ€™ve tightened up the building and added an air intake for the boiler (it was burning indoor air before).
Actual in-wall insulation is non-existent. Thatâ€™s in the 5 year plan. The structure is 4 stories about 4500 sq ft and brick faced. There are also 63 windows in the buildingâ€¦great for lightâ€¦.lousy for heat.

â€œIt could shut off for over temperatureâ€. Donâ€™t think this is the problem since boiler never reaches temp above 70 degrees before it turns off (and I have checked flow to individual radiators and it appears fine).

Againâ€¦I donâ€™t know that this is relevantâ€¦.but eventually after cycling enuff times (maybe for 2 â€“3 hours) it gets to temp and seems to run fine. Itâ€™s like the lower the indoor temperature is....the more likely it is to run continuouslyâ€¦this is the reason I thought thermostat first. [Which I picked up today and will install tomorrow]

Ohâ€¦one more thingâ€¦I havenâ€™t personally seen the bills but Iâ€™ve been told the gas bill can hit $1000 per month in the dead of winter in Lincoln Nebraska in this building. It just seems high to me even based on all of the other factors noted. PS. I observed individual apartments and windows and noted almost NO open windows due to excess heat last winter.

I am not a heating person, but I believe what should happen is the thermostat controls the pump and the boiler reacts to water temp. The pump and flame ought not to always run at the same time in a boiler with a large amount of water in the boiler itself. Probably the case in a boiler as old as yor have.

You really ought to have someone look at it. Go to heatinghelp.com for advice and a listing of pros that might be in your area.

That makes sense....but it brings one additional (fundamental) question to mind...and again I apologize because I have no experience with boilers....

does a boiler always have water at temperature (essentially constant temp) throughout the entire heating part of the year. IE if the thermostat is not turning on the pump....the boiler will still maintain a constant temperature supply of water.

[As a side, this is my second season in this apartment....I suspect someone miswired something in the past and it has contributed to the unusually high heating bills.]

Some boilers attempt to maintain a set internal water supply temp, some don't. The old ones typically have a large volume of water in the boiler, the new ones don't. Hard to tell for sure.

With no insulation in the walls and all of those windows, $1000 might not be that far out of line depending on your price schedule. I've seen bills of over $120 on a winter month for a small, insulated condo and I've only got two outside walls.

The boiler only controls water temp. Your thermostats control the pump and zone valves at each radiator. Water temp drops, the boiler fires, regardless of room temp. You mentioned a pump so we know its not a steam system. You could have a crudded up boiler, or a bad water temp thermal switch. If this unit is really 50 years old, you would benefit greatly by a new boiler. If your fuel bills are honestly $1000 a month, a new unit could very easy cut this in half or maybe more, especially if the boiler provides domestic hot water as well. 50 years ago nobody cared about effeciency. Fuel was cheap, buildings were drafty, so why care anyway? New units can be as much as 90 percent effiecient, (many vent through pvc pipe instead of steel stove pipe and a flue) while you might be looking at 40-50 on your 50 year old unit. Add 50 years of wear and tear, 50 years of rust and crud build up, and cut that effeciency in half again. A new unit could pay for itself very rapidly.